1. Field of the Invention
The present invention relates to a circuit arrangement for controlling power semiconductor transistors, often used in power switches and circuit breaker type devices. More specifically, the present invention relates to a circuit arrangement for controlling a power semiconductor transistor through the use of at least two mirror-symmetrical power sources resulting in a faster commutation with a linear current voltage response.
2. Description of the Related Art
Power transistors such as IGBTs (Insulating-Gate Bipolar Transistors) or MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) are conventionally known. In use, power transistors such as IGBTs are regulated, i.e. switched into a conductive or non-conductive state, by applying a certain voltage between the gate and the emitter.
To switch the transistor into a conductive state, i.e. allowing power flow between the collector and the emitter, the gate is charged with the applied voltage.
To switch the transistor into the non-conductive state, the gate is reversed, i.e. charged with the other polarity. This happens, for example, in IGBTs when a voltage of opposite polarity is applied between the gate and the emitter.
These switching processes, from a conductive to non-conductive stage or vice versa are also called commutation.
It should be understood, that in the following description, the same relationships as described for an IGBT also apply to the corresponding connections—drain and source—of a MOSFET component, although a MOSFET is usually switched into the non-conductive state by applying a zero voltage.
Power transistors can be controlled according to different control principles. These different control principals include gate control via resistor control circuits, via voltage control circuits and via current control circuits. The most common of these is the resistor control circuit. Characteristic for such a control circuit is the formation of a so-called Miller plateau in the time path or time progression curve of the voltage between gate and emitter during a commutation process. The supply of the gate in the time path after the passage of the Miller plateau generally shows the path of a curve with a non-linear (1-exp(-t)) dependence.
Referring now to FIG. 1, a simulation of the time path of a gate-emitter voltage VGE and of a charging current IO of the gate with resistor control according to the conventional art is shown during a commutation process. At a beginning of the commutation process, at approximately 0.5 μs, the charging current IO increases sharply while the voltage VGE rises almost linearly along V11. After about 0.5 μs, the Miller plateau V,12 is reached, whose time expansion or duration is about 0.7 μs. During this time, the charging current IG is also constant. During the further progression along V13, the gate-emitter voltage VGE increases until it reaches the expected value with a non-linear slope (1-exp(-t)) characteristic, as earlier noted. In total, the expected value of 15 V is reached after about 6 μs. During that time, the charging current IG also drops in a corresponding and characteristic fashion.
As can be easily seen from FIG. 1, one disadvantage of controlling gate control circuits via resistor control or voltage control circuits is the necessity of a stabilized supply voltage source. This is an inevitable requirement to keep the power losses of the power transistor (which requires a defined gate voltage) low.
Another disadvantage of the time path of the non-linear charge curve of the gate (after the Miller plateau) is that the curved response necessarily delays the switching process of the power transistor. The power transistor does not switch at the rate to which it would be technically able. This delay in switching time results in disadvantageous switching power losses.
Another unfortunate consequence of the above-mentioned curved time response path is that a collector-emitter voltage, which in the conventional art is not active during the switching process itself, can only be activated with a delay necessitated and caused by the curved response time path failing to timely meet its required value.